There has been generally known a conventional imaging apparatus having a structure in which a photoelectric conversion element for photoelectrically converting incident light also serves as an accumulating portion for accumulating electric charges.
On the other hand, Japanese Patent Application Laid-Open No. 2006-246450 discloses a technique of transferring electric charges generated in the photoelectric conversion element to a charge accumulating region without accumulating the electric charges in the photoelectric conversion element in a structure in which a charge accumulating portion is provided separate from the photoelectric conversion element. FIGS. 12A to 12G correspond to FIG. 6 cited from Japanese Patent Application Laid-Open No. 2006-246450. A MOS transistor is used in which a transferring portion between the photoelectric conversion element and the charge accumulating portion has a buried channel structure. According to Japanese Patent Application Laid-Open No. 2006-246450, the photoelectric conversion element can be maintained at a minimum size required to receive light. Therefore, it is possible to realize an in-plane synchronized electronic shutter in which charge accumulation start times and charge accumulation end times of all in plane pixels are matched.
However, according to Japanese Patent Application Laid-Open No. 2006-246450, electric charges generated in the photoelectric conversion element at a timing of FIG. 12E and subsequent timings are discharged into an overflow drain (hereinafter referred to as OFD), and hence studies for using the electric charges that have overflown to the OFD as signals were not sufficiently made. In general, when a plurality of images are to be successively obtained as in a case of taking a moving image, electric charges generated in the photoelectric conversion element during a time period for which signals corresponding to one image (frame) are read out from the accumulating portion are also required to be used for a signal for forming an image. In the technology disclosed in Japanese Patent Application Laid-Open No. 2006-246450, the signals generated during the time period are discharged into a power source. Therefore, sensitivity may become insufficient or no smooth moving image may be obtained.
On the other hand, when a still image is to be taken, it is required to match charge accumulation start timings and charge accumulation end timings of all pixels for outputting signals for forming an image.